Loss Analysis of a 24.4%-Efficient Front-Junction Silicon Heterojunction Solar Cell and Opportunity for Localized Contacts

Silicon heterojunction (SHJ) solar cells have recently reached power conversion efficiencies above 25% with various device architectures and with industrial size (>200 cm²) wafers. Yet, for an accurate assessment of the efficiency potential and further development of the technology, the identification of high-performing device configurations, and their detailed analysis is still vital. In this work, we first present an overview of our lab-scale (4 cm²) front-junction cells based on n-type wafers with a 24.44% certified efficiency. We report on the key improvements compared with our previously reported devices (i.e., thinner front-side silicon layers and low refractive index rear reflector). Then, we present a detailed power loss analysis, showing that parasitic absorption in the front layer-stack remains a major source of loss despite the recent improvements. Accordingly, we investigate next approaches to circumvent this loss, such as localization of the highly absorbing front layers and switching to a rear-junction architecture. Using numerical calculations, we show that the front-junction configuration can benefit from an efficiency gain of 0.3%_abs with contact localization if considerably low contact resistivities (<20 mΩ·cm²) are realized for the p-type contact. Even larger gain in efficiency can be achieved by simultaneously switching to a rear-junction architecture and localizing the n-type contact with contact resistivities that are relatively accessible with the current state of the art (up to 0.7%_abs gain for <20 mΩ·cm²). Finally, we propose a simple fabrication method for contact localization using shadow masks during depositions of the front-side layers and demonstrate proof-of-concept cells with localized contacts.